Expositor: Scriptable time-travel debugging with first-class traces

Abstract

Abstract-We present EXPOSITOR, a new debugging environment that combines scripting and time-travel debugging to allow programmers to automate complex debugging tasks. The fundamental abstraction provided by EXPOSITOR is the execution trace, which is a time-indexed sequence of program state snapshots. Programmers can manipulate traces as if they were simple lists with operations such as map and filter. Under the hood, EXPOSITOR efficiently implements traces as lazy, sparse interval trees whose contents are materialized on demand. EXPOSITOR also provides a novel data structure, the edit hash array mapped trie, which is a lazy implementation of sets, maps, multisets, and multimaps that enables programmers to maximize the efficiency of their debugging scripts. We have used EXPOSITOR to debug a stack overflow and to unravel a subtle data race in Firefox. We believe that EXPOSITOR represents an important step forward in improving the technology for diagnosing complex, hard-to-understand bugs.

Time-Traveling Debugging Queries: Faster Program Exploration

“…On the other hand, there are other projects that do research on how to exploit them [KM04], [KM08], [PFH13], for program comprehension and debugging. This is where we position our work, and compare similarities against related research projects listed in the following paragraphs.…”

“…Our work shares similarities with Expositor [PFH13]. Like our solution, Expositor combines scripting and time-travel debugging to allow programmers to automate complex debugging tasks.…”

“…To test their hypotheses, they try to reproduce the bug by observing data and behavior supporting such hypotheses. Facing a wrong hypothesis forces developers to formulate new, more refined ones, iteratively narrowing down the possible cause [Spi18], [Zel09], [O'D17], [BM14], [PFH13].…”

Sindarin: a versatile scripting API for the Pharo debugger

“…Expositor [32], inspired by the work on MzTake [28], combines scripting and time-travel debugging. The fundamental abstraction provided by Expositor is the execution trace, which is a time-indexed sequence of program state snapshots.…”

“…A line of research has also started to study scripting APIs to empower developers to implement debugging scripts adapted to their needs. These scripting APIs help developers to e.g., insert breakpoints based on cross-cutting concerns [42] or declaratively explore post-mortem executions [32]. Even further, the moldable debugger framework [6] allows developers to create domain-specific debuggers with domain-specific views and operations.…”